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Diffstat (limited to 'Documentation/usb/URB.txt')
| -rw-r--r-- | Documentation/usb/URB.txt | 21 |
1 files changed, 10 insertions, 11 deletions
diff --git a/Documentation/usb/URB.txt b/Documentation/usb/URB.txt index 00d2c644068..50da0d45544 100644 --- a/Documentation/usb/URB.txt +++ b/Documentation/usb/URB.txt @@ -195,13 +195,12 @@ by the completion handler. The handler is of the following type: - typedef void (*usb_complete_t)(struct urb *, struct pt_regs *) + typedef void (*usb_complete_t)(struct urb *) -I.e., it gets the URB that caused the completion call, plus the -register values at the time of the corresponding interrupt (if any). -In the completion handler, you should have a look at urb->status to -detect any USB errors. Since the context parameter is included in the URB, -you can pass information to the completion handler. +I.e., it gets the URB that caused the completion call. In the completion +handler, you should have a look at urb->status to detect any USB errors. +Since the context parameter is included in the URB, you can pass +information to the completion handler. Note that even when an error (or unlink) is reported, data may have been transferred. That's because USB transfers are packetized; it might take @@ -210,12 +209,12 @@ have transferred successfully before the completion was called. NOTE: ***** WARNING ***** -NEVER SLEEP IN A COMPLETION HANDLER. These are normally called -during hardware interrupt processing. If you can, defer substantial -work to a tasklet (bottom half) to keep system latencies low. You'll -probably need to use spinlocks to protect data structures you manipulate -in completion handlers. +NEVER SLEEP IN A COMPLETION HANDLER. These are often called in atomic +context. +In the current kernel, completion handlers run with local interrupts +disabled, but in the future this will be changed, so don't assume that +local IRQs are always disabled inside completion handlers. 1.8. How to do isochronous (ISO) transfers? |